Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus including the zoom lens, which are suitable for an image pickup optical system of an image pickup apparatus, such as a video camera, a digital still camera, a film camera, a broadcasting camera, or a monitoring camera.
Description of the Related Art
In recent years, as an image pickup optical system used for an image pickup apparatus, there is a demand for a zoom lens having a high aperture ratio, a high zoom ratio, and a high optical characteristic over an entire object distance from infinity to close distance.
In the related art, as a focusing method of a zoom lens, there have been known a so-called front lens focus system in which a first lens unit arranged closest to an object side is moved, and a so-called inner focus system (rear focus system) in which lenses arranged on an image side of a first lens unit are moved. In general, a zoom lens using the inner focus system has a smaller beam effective diameter of the first lens unit than that of a zoom lens using the front lens focus system, and hence is easy to downsize the entire lens system. In addition, a lens unit that is relatively small in size and weight is moved to perform focusing, and hence it is easy to realize an increase in speed of the focusing.
In the related art, there has been known the zoom lens using the inner focus system. In each of Japanese Patent Application Laid-Open No. 2005-292338 and Japanese Patent Application Laid-Open No. 2012-78788, there is disclosed a zoom lens including, in order from an object side to an image side, a first lens unit to a fifth lens unit having positive, negative, positive, positive, and negative refractive powers, in which each of the lens units is moved during zooming, and the fourth lens unit is moved during focusing. In addition, in Japanese Patent Application Laid-Open No. 2003-255228, there is disclosed a zoom lens including, in order from an object side to an image side, a first lens unit to a fifth lens unit having positive, negative, positive, negative, and positive refractive powers, in which each of the lens units is moved during zooming, and the fifth lens unit is moved during focusing.
In order to realize the increase in speed of the focusing in the zoom lens using the inner focus system, it is important to appropriately set the refractive power of each of the lens units forming the zoom lens and a refractive power of a focus unit.